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Stock-Based Compensation - Summary of Changes in Status of Performance RSUs' (Parenthetical) (Detail) (Performance-Based Restricted Stock [Member])
 12 Months Ended
Dec. 31, 2014
TSR Portion [Member]
  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Adjustment percentage used for Performance awards 50.00%ed_ShareBasedCompensationArrangementPercentageOfRsu
/ us-gaap_AwardTypeAxis
= ed_PerformanceBasedRestrictedStockMember
/ us-gaap_PlanNameAxis
= ed_TsrPortionMember
Non-TSR Portion [Member]
  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Adjustment percentage used for Performance awards 50.00%ed_ShareBasedCompensationArrangementPercentageOfRsu
/ us-gaap_AwardTypeAxis
= ed_PerformanceBasedRestrictedStockMember
/ us-gaap_PlanNameAxis
= ed_NonTsrPortionMember